1. Field of the Invention
The present invention relates to a switching regulated power supply apparatus. More specifically, the present invention relates to an improved switching regulated power supply apparatus wherein a direct current voltage obtained through rectification and smoothing of a commercial alternate current power supply input is applied to a direct current/alternate current converting circuit implemented by a switching device to convert the said direct current voltage into an alternate current voltage such that the ratio of the on and off time periods of the said switching device is controlled, whereupon the converted alternate current output is rectified and smoothed to provide a direct current constant voltage.
2. Description of the Prior Art
A variety of types of switching regulated power supply apparatuses were proposed and put into practical use. Such switching regulated power supply apparatuses may be classified depending on the type of the direct current/alternate current converting circuit, a driving system of the switching device, a circuit configuration of the constant voltage control, and the like. In particular, such switching regulated power supply apparatuses may be classified into an externally excited driving system and self excited driving system from the stand point of the above described driving system of the switching device. More specifically, the externally excited driving system may be defined as a switching regulated power supply apparatus wherein a switching device in a direct current/alternate current converting circuit for on/off controlling the input voltage supplied thereto is adapted to be driven in response to an output from an external oscillator, and a self excited driving system may be defined as a switching regulated power supply apparatus wherein a self running oscillator is formed to trigger the switching device so that the switching device does not require any external triggering signal.
The externally excited switching regulated power supply apparatus has advantages that the above described switching device may be of a type of a small peak current and a converter transformer to be connected to the switching device may be small sized. Nevertheless, this type of switching regulated power supply apparatus requires a transformer coupled driver circuit provided between the above described external oscillator and the switching device, which driver circuit usually comprises a control circuit for controlling the ratio of the on and off time periods of the switching operation. As a result, the type of the control circuit is restricted and the number of components as a whole in the power supply apparatus is increased, which makes the circuit configuration of the apparatus complicated. In addition, the external oscillator need be directly driven with the commercial alternate current power supply input at least at the start of the operation, which causes an increased power loss at the start of operation.
On the other hand, the self excited switching regulated power supply apparatus can be dispensed with an external oscillator and a driver circuit, which makes the circuit configuration of the apparatus simple and reduce the power loss at the start of operation. Nevertheless, this type of the switching regulated power supply apparatus has shortcomings that the switching frequency of the switching device is liable to vary depending on fluctuation of the power supply input and the load to cause an unstabilized constant voltage operation and a switching device of a large peak current must be used.
From the stand point of safety to the users and service engineers of the laws and rules in some countries in the world impose a strict requirement in connection with insulation of electrical machines and in particular complete insulation of a built-in power supply apparatus at the output side thereof from the commercial power source line. Nevertheless, the prior art switching regulated power supply apparatus involves the above described advantages and disadvantages depending upon which type is employed, a self excited driving system or externally excited driving system. Therefore, taking into consideration the insulation between the input and output of the power supply apparatus, selection of a self excited driving system or externally excited driving system is of a great problem in designing a switching regulated power supply apparatus.
The present invention was accomplished for the purpose of eliminating the above discussed problems encountered in conjunction with the prior art switching regulated power supply apparatus.